Parametric optimization of the algorithm (SVM and RF)
ML models’ performance is influenced by their parameters, making it essential to optimize the parameters by pre-setting the value of MSE. There are several methods adopted to address the poor prediction accuracy and acquire the optimal parameter.
(1) There are two ways to adjust the network parameters of the BPNN: (a) Determining the minimum MSE value by comparing different numbers of hidden layers or nodes in the hidden layer to obtain the optimal parameters. (b) Algorithms of PSO and GWO were combined for parameter optimization and the optimization ability of two methods was compared inFigure 17 .
(2) The penalty coefficient c and gamma g play an important role in the SVM model, where c determines the generalization ability and g affects the prediction accuracy. The libSVM toolbox (Chang and Lin, 2001) is adopted for parameter optimization of c and g , the process of which is shown inFigure 9 (a).
(3) In RF model, leaves’ number has an impact on the prediction accuracy and grown trees determine whether the model will be over-fitted. The process of optimization are shown in Figure 9 (b).
(4) The optimal number of nodes of the hidden layer is needed to be determined in the ELM. Therefore, the models’ optimization search is completed by pre-setting MSE.
(5) The XGB optimizes parameters through regularization, cross-validation, and so on.

4.2 ML predictive performance analysis

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Figure 10 Comparison of predicted and observed Q0.3
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Figure 11 Comparison of predicted and observed Q5
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